The effects of size and pigmentation of two species of Chaoborus on the predation rates and selectivity of Lepomis gibbosus.

Abstract

Morphological characteristics of prey can affect the selectivity and rates of predator response. The color and size of two species of Chaoborus, a type of zooplankton, were varied in order to test for differences in the responses of Lepomis gibbosus, the pumpkinseed sunfish. Chaoborus flavicans, the larger of the two zooplankton, and Chaoborus punctipennis were fed to the pumpkinseeds in a number of trials in which some of the organisms were dyed. The zooplankton were dropped individually or in pairs into tanks containing the pumpkinseeds. The individual trials tested the mean response times of the fish and the paired trials examined predator selectivity. The results show that the larger species of Chaoborus was generally eaten more quickly than the smaller species and that dyed zooplankton were also more quickly selected by the fish. While both factors of color and size seem to play a role in determining predator response, according to our data, size is a more important determinant that pigmentation.